The present invention relates to a control apparatus of a premixed charge compression ignition engine, which includes an engine body having a cylinder in which mixture gas self-ignites within at least one of operating ranges of the engine.
Conventionally, a study is conducted about performing premixed charge compression ignition combustion in the engine, in order to improve fuel consumption. In the premixed charge compression self-ignition combustion, fuel and air are premixed to form a mixture gas and the mixture gas is compressed to self-ignite.
However, for example, when an engine load is high, an issue of producing more smoke arises due to the mixture gas igniting before the fuel is sufficiently mixed with air, and further, an issue of worsening combustion noise arises due to an increase in pressure inside the cylinder of the engine.
In this regard, a study is conducted about performing Exhaust Gas Recirculation (EGR) in which EGR gas (a portion of the exhaust gas) is recirculated to an intake passage, to introduce an inactive gas which is neither fuel nor air into the cylinder. In this manner, an ignition delay time of the mixture gas is extended, and as a result, the mixing of the fuel and air is stimulated. JP2009-209809A discloses such an art.
However, there is a limit to the extending effect of the ignition delay time which can be obtained by introducing the EGR gas, and within an engine operating range where an engine load is high, it becomes difficult to secure a suitable length of ignition delay time by the EGR gas introduction. Specifically, within the operating range where the engine load is high, since an amount of air required for combustion becomes large, to recirculate a large amount of EGR gas while securing the air amount, a forced induction needs to be performed, which increases pressure inside the cylinder. However, the ignition delay time becomes shorter as the pressure inside the cylinder increases. Therefore, within this operating range, even if the large amount of EGR gas is recirculated, the ignition delay time may not be extended sufficiently.